1. Field of the Invention
The present invention relates to the macroporous manganese oxide having ferromagnetic property and a method of preparing the same, more particularly to the macroporous ferromagnetic manganese oxide having three-dimensionally-ordered nanopores, which is prepared by aligning polymer colloidal particles with an average diameter of a few hundred nanometers, infiltrating a solution of the precursor compound capable of forming the manganese oxide represented by the following Chemical Formula 1 into interstices of the colloidal template, heating in an oxygen atmosphere to decompose and remove the polymer particles, and a method for preparing the same:La1-xCax-ySryMnO3 (1)
wherein 0.25<x<0.35 and 0<y≦0.35.
2. Description of Related Art
Only iron and a few other metals such as cobalt, nickel, and gadolinium can be made into strong magnets. These materials are said to be ferromagnetic. In addition, various iron oxides have also been known to have ferromagnetism from the ancient times. Accordingly, the ferromagnetic materials have been used as compasses and other useful tools. Ferromagnetism is not limited to iron-containing metal oxides, and is also found in other transition metal oxides with unpaired electrons. For example, a manganese oxide with perovskite structure shows ferromagnetism and also has conducting property. Heating a magnet can cause a loss in magnetism, for raising the temperature increases the random thermal motion of the atoms that tends to randomize the domains. Above a certain temperature known as the Curie temperature, a magnet cannot be made at all. The Curie temperature depends on the kind of metal. Generally, compounds containing iron have high Curie temperature. Iron oxide shows a ferromagnetic transition typically over 400 K and also has large saturated magnetic moment.
Since the ferrites have ferromagnetism but are insulating, their applications are limited to microwave devices or permanent magnets. On the contrary, the manganese oxides with perovskite structure show metal-insulator transition around the Curie temperature. They have metallic property in the ferromagnetism range while they are insulating in the paramagnetic region, namely above the Curie temperature. The Mn-based perovskite oxide is known to be colossal magneto resistance (CMR) material, which shows rapid decrease in resistance near the Curie temperature upon applying a magnetic field. Accordingly, researches on the manganese oxides have been focused until now on industrial application of this magneto resistance property. In this regard, many researches have been conducted to develop devices like magneto resistance sensors.
On the other hand, there have been few researches on application of the manganese oxides in magnetic filters or photonic devices. It is largely because manganese oxides are not hard enough to maintain their framework and also it is difficult to form pores inside the materials. If we can make such a strong manganese oxide, it can be used as magnetic filters or photonic devices. Because filters currently used are primarily made of silicon oxide or aluminum oxide, they cannot capture magnetic nanoparticles effectively. If the manganese oxide material is used with ferromagnetism as a filter, it can remove magnetic ions completely. Moreover, if pores having a diameter of several nanometers are highly ordered, it can be useful for photonic devices.